The detail description about peripheral nervous system, neuron, its covering, types of neuron, synapses, spinal nerves, plexus, and more about cranial nerves at last not the least about somatic and autonomic nervous system. you may also find the information about types of peripheral nervous system in detail.

1. The peripheral nervous system
Shehzad Hussain
6/7-June-2017

2. Contents:
1. Introduction
2. Types of PNS
3. Spinal nerves
4. Neuron and its basic function
5. Types of neuron (3 basic types)
6. Synapsis
7. Somatic nervous system
8. Spinal nerves
9. Plexus
10. Cranial nerves
11. Autonomic nervous system

3. Introduction:
• The peripheral nervous system (PNS) is one of the two main
parts of the nervous system, the other part is the central
nervous system (CNS). The PNS consists of
the nerves and ganglia outside of the brain and spinal
cord. The main function of the PNS is to connect the CNS to
the limbs and organs, essentially serving as a relay between
the brain and spinal cord and the rest of the body.

4. Cont…
• These nerves extend from the central nervous system to the
outermost areas of the body.
• The nervous system is divided into the
o Peripheral nervous system (PNS)
o Central nervous system (CNS)

5. Concept Map
which consists of
is divided into
that make up
which is divided into
Section 35-3
The Nervous
System
Sensory nervesMotor nerves
Autonomic nervous
system
Somatic nervous
system
Central nervous
system
Peripheral nervous
system
Sympathetic
nervous system
Parasympathetic
nervous system

6. Type of PNS
• The peripheral nervous system is divided into
the somatic nervous system and the autonomic nervous
system. In the somatic nervous system, the cranial
nerves are part of the PNS.
1. Motor Division – impulses from CNS to muscles or
glands
• Two Parts:
– Somatic Nervous System
– Autonomic Nervous System
2. Sensory Division – transmits impulses from sense
organs to CNS

7. Cont…
• The peripheral nervous system is divided into
the somatic nervous system, and the autonomic
nervous system. The somatic nervous system is under
voluntary control, and transmits signals from the brain
to end organs such as muscles. The sensory nervous
system is part of the somatic nervous system and
transmits signals from senses such as taste and touch
(including fine touch and gross touch) to the spinal
cord and brain. The autonomic nervous system is a
'self-regulating' system which influences the function
of organs outside of voluntary control, such as
the heart rate, or the functions of the digestive system.

8. Spinal nerves
• Peripheral Nervous System consists of:
• i) 31 pairs of Spinal Nerves
• Ii) 12 pairs of Cranial Nerves.
• There are 31 pairs of spinal nerves that leaves the vertebral
canal (formed by 33 vertebrae) by passing through the
intervertebral foramina. They are named and grouped
according to the vertebrae with which they are associated:
 8 cervical
 12 thoracic
 5 lumbar
 5 sacral
 1 coccygeal

9. Neuron
• Neurons are made up of the following parts:
– The nucleus (which contains the genetic organelles)
– The soma (or cell body)
– Dendrites (branch-like structures which receive
information from other neurons)
– Axons (long tubular pathways which send information to
other parts of the brain)
– An (axonal) presynaptic terminal. The presynaptic terminal
connects to other neurons via synapses. Many axons are
surrounded by myelin, essentially sheaths which help
axons quickly send signals over long distances.

11. Electron microscope photograph of a neuron

12. Covering of a neuron:
Each nerve consists of bundles of nerve fibers each of
which is covered with fine connective tissues, which is;
1. Endoneurium: is a layer of delicate connective tissue
around the myelin sheath of each myelinated nerve
fiber.
2. Perineurium: Nerve fibers are bundled together into
groups known as fascicles, each surrounded by a
protective sheath known as the perineurium.
3. Epineurium: is the outermost layer of dense irregular
connective tissue surrounding a peripheral nerve.

14. Basic types of neurons
Neurons are divided on the basis of structures
and size.
There are 3 different types of neurons:
Multipolar neurons: one axon, many
dendrites
Bipolar neurons: one axon, one dendrite
Pseudounipolar neurons: One process that
branches in two.

17. 1. MULTIPOLAR NEURONS.
• These neurons contain a number of dendrites and
one axon. They are the most common type
of neurons and they can be found more or less
anywhere in the nervous system.
For example:
• Pyramidal neurons in the cerebral cortex
• Purkinje neurons in the cerebellum
• Motor neurons in the anterior horn of the spinal
cord

18. 2. BIPOLAR NEURONS
• Bipolar neurons have only two process that connect
to the cell body: one dendrite and one axon. (This is
easy to remember as, generally speaking, the prefix
“bi” refers to the number two, such as in bilingual –
two languages)
• Bipolar neurons are only found in specific areas of
the nervous system:
• In the retina
• In the nose (receptors of the olfactory epithelium)

19. 3. PSEUDOUNIPOLAR NEURONS
• There is only one process (this gives us the “unipolar
part”) that branches into two (which is why we add
“pseudo” at the beginning… It doesn’t look
unipolar). This process is structurally similar to that
of an axon, but it can receive information as well.
• Pseudounipolar neurons can be found in the
spinal ganglions.

20. TYPE A FIBERS TYPE B FIBERS TYPE C FIBERS
Thickest and fastest
conducting fibers.
Medium in size Smallest and thinnest
Myelinated. Myelinated. Non-myelinated.
diameter 1.5-20 micron diameter 1.5-3.5 microns. diameter 0.1-2 microns.
speed of conduction is 4-
120 m/sec
speed of conduction is 3-15
m/sec
speed of conduction is 0.5-
4 m/sec

21. MINIMUM POINTS TO REMEMBER:
• Neurons are the type of cells. They are made
of:
• A cell body-called the soma
• Dendrites that receive information
• An axon that transmits information to
another cell.
• Neurons are polarized in that the information
can only travel in one direction: dendrite to
axon.

22. Synapsis:
There are 3 types of
synaptic connections
between 2 neurons:
a) Axodendritic
b) Axosomatic
c) Axoaxonic

23. Function:
• The primary role of nerve is to transmit
information reliably from the anterior horn cells
to muscles for motor system (Efferent Pathway)
& from the sensory receptors to the spinal cord
or CNS for the sensory system (Afferent Pathway)
• Although functionally nerves may seem similar
to electrical wires, there are vast differences
between them.
• At the molecular level, a complex set of chemical
and electrical events allows nerve to propagate
an electrical signal.

24. Branches:
• Immediately after emerging from the intervertebral
foramina spinal nerves divide into branches, or rami:
posterior ramus and anterior ramus.
• Posterior ramus supply skin and muscles of back and
anterior ramus forms the plexus.
• There are five large plexuses of mixed nerves formed on
each side of the vertebral column”:
1. Cervical
2. Brachial
3. Lumbar
4. Sacral
5. Coccygeal

26. Cont…
The definition of the peripheral nervous system generally
includes the peripheral nerves, their primary motor and
sensory neurons, neuromuscular junctions (NMJs), and
muscles (Figure 2-1). In addition, cranial nerves II to XII
usually are included in the peripheral nervous system,
being essentially the same as peripheral nerves except
that their primary motor neurons are located in the
brainstem rather than the spinal cord. The primary motor
neurons, the anterior horn cells, are located in the ventral
gray matter of the spinal cord. The axons of these cells
ultimately become the motor fibers in peripheral nerves.

27. Cont…
Their projections first run through the white matter
of the anterior spinal cord before exiting ventrally
as the motor roots In contrast to the anterior horn
cell, however, the primary sensory neuron, the
dorsal root ganglion (DRG), is not found within the
substance of the spinal cord itself but lies outside,
near the intervertebral foramen. The dorsal root
ganglia are bipolar cells with two separate axonal
projections. Their central projections form the
sensory nerve roots.

28. • The sensory roots enter the spinal cord on the
dorsal side to either ascend in the posterior
columns or synapse with sensory neurons in the
dorsal homo The peripheral projections of the
DRGs ultimately become the sensory fibers in
peripheral nerves. These anatomic differences
between the anterior horn cells and dorsal root
ganglia result in a different pattern of motor and
sensory nerve conduction abnormalities,
depending on whether the lesion is in the
peripheral nerve or proximal to the DRG at the
root level.

30. Cont…
Motor and sensory roots at each spinal level unite
distal to tile DRG to become a mixed spinal nerve.
There are 31 pairs of spinal nerves (8 cervical, 12
thoracic, 5 lumbar, 5 sacral, I coccygeal. Each spinal
nerve divides into a dorsal and ventral ramus.
Unlike the dorsal and ventral nerve roots, the dorsal
and ventral rami both contain motor and sensory
fibers. The dorsal ramus runs posteriorly to supply
sensory innervation to the skin over the spine and
muscular innervation to the paraspinal muscles at
that segment.

36. Cranial nerves:
• Cranial nerves are the nerves that emerge directly
from the brain (including the brainstem), in contrast
to spinal nerves (which emerge from segments of
the spinal cord). 10 of 12 of the cranial nerves
originate in the brainstem. Cranial nerves relay
information between the brain and parts of the body,
primarily to and from regions of the head and neck.
• The terminal nerves, olfactory nerves (I) and optic
nerves (II) emerge from the cerebrum or forebrain,
and the remaining ten pairs arise from the
brainstem, which is the lower part of the brain.

38. Function:
• Smell (I)
• Vision (II)
• Eye movement (III, IV, VI)
• Trigeminal nerve ( sensation to the skin of the face) (V)
• Facial expression (VII)
• Hearing and balance (VIII)
• Oral sensation, taste, and salivation (IX)
• Vagus nerve (blood pressure and heart rate) (X)
• Shoulder elevation and head-turning (XI)
• Tongue movement (XII)

40. Autonomic Nervous system:
• The autonomic or involuntary part of the
nervous system controls the autonomic
function of the body. i.e. initiated below the
level of the cerebrum. The effect of autonomic
activity are rapid and the effectors organs are:
• Smooth muscles( change in airway or blood
vessel diameter)
• cardiac muscle(changes in heart rate)
• glands(increase or decrease secretion)

41. The Autonomic Nervous System:
• Regulate activity of smooth muscle, cardiac
muscle & certain glands
• Structures involved
1. general visceral afferent neurons
2. general visceral efferent neurons
3. integration center within the brain
• Receives input from limbic system and other
regions of the cerebrum.

42. Autonomic versus Somatic NS
• Somatic nervous system
– consciously perceived sensations
– excitation of skeletal muscle
– one neuron connects CNS to organ
• Autonomic nervous system
– unconsciously perceived visceral sensations
– involuntary inhibition or excitation of smooth muscle,
cardiac muscle or glandular secretion
– two neurons needed to connect CNS to organ
• preganglionic and postganglionic neurons

43. Autonomic versus Somatic NS
• Autonomic NS pathway is a 2 neuron pathway
• Somatic NS pathway only contains one neuron.

44. 44
Basic Anatomy of ANS
• Preganglionic neuron
– cell body in brain or spinal cord
– axon is myelinated type B fiber that extends to autonomic ganglion
• Postganglionic neuron
– cell body lies outside the CNS in an autonomic ganglion
– axon is unmyelinated type C fiber that terminates in a visceral
effector

45. Sympathetic Nervous System:
• The sympathetic nervous system
originates in the spinal cord and its main
function is to activate the physiological
changes that occur during the fight or
flight response.
• This component of the autonomic nervous
system utilizes and activates the release of
norepinephrine in the reaction.

46. Parasympathetic Nervous System:
• The parasympathetic nervous system
originates in the spinal cord and medulla and
works with the sympathetic nervous system.
• Its main function is to activate the "rest and
digest" response and return the body
to homeostasis after the fight or flight
response.
• This system utilizes and activates the release of
the neurotransmitter acetylcholine